Cape Vulture. Slower wingbeat and flight speed make them an easier subject. Canon EOS 1D MkIV, Sigma EX 120-300 f2.8 HSM, 300mm, 1/2000, f4, ISO 100

Ask any three nature photographers how to do birds in flight, and you’ll probably get three different responses.  Everyone who do this has developed a method that works for them.  Usually it is dependent on type and model of camera body, same for the lens in use and their own personal skills level.
So to cut to the chase – the best way to do birds in flight:  buy the most top of the line camera body from one of the major brands, buy the fastest focussing, fastest aperture lens of a telephoto type available on the planet, then spent hours learning to set up that camera, practise for hours and hours the proper panning and tracking techniques, then pray for the best of luck and go get that bird in flight.
But if you don’t have an unlimited budget and endless hours of free time, don’t despair.  There are certainly ways in which you can become more adept at this “birds in flight” thing, using your current equipment.  It must be said that higher end equipment will make a difference in your results but using more entry level camera bodies and lenses do not mean you will not have success.  It merely means you must work harder at it and expect a lower rate of success in comparison to the well- equipped pro photographer.

White-bellied Sunbird, timed to capture the launch. Canon EOS 1D X MkII, Sigma EX 300-800 f5.6 HSM, 800mm, 1/2500, f5.6, ISO 800

To get the odds in your favour I would suggest you take heed of some tips and tricks I have picked up over the years.  First of all is to set up your camera properly by using the servo focus tracking system of your camera, and also setting multi shot mode (motor drive / continuous advance / many frames per second mode.)  Using the back-button focus technique is certainly worth considering, it helps the AF algorithms of your camera to continuously track a moving subject easier.  The camera mode can be set to your preference, I suggest start off with Aperture Priority mode initially with the lens set to f7.1 or f8, and an ISO setting to ensure a fast enough shutter speed, 1/1000 or faster.  This will lessen errors due to camera shake, irregular panning etc which can all lead to soft images.  If your camera and lens combo is light enough to handhold easy, then do that.  Otherwise think about mounting it on a monopod or tripod, the latter being my last option.  Remember that the closer the subject is to you, the faster his in-frame speed will be and thus making it more difficult to keep tracking him.
Once your camera is set up properly, identify and concentrate on your quarry, learn its behavioural characteristics, and obviously where to find them.  Start with the easier birds to capture in flight, and a rule of thumb is bigger is better.  The larger birds usually have slower wingbeats, fly more predictable flight patterns and are therefore easier to track and keep in the frame.  Being larger subjects, they also fill the frame easier even when photographing them at a distance. I suggest you definitely try for the bigger Herons and Vultures first before going for Swifts and Swallows.

Black-headed Heron also has a slow wingbeat. Canon EOS 1D MkIV, Sigma EX 120-300 f2.8 OS with 2x TC, 429mm, 1/4000, f5.6, ISO 400

The medium-sized Egrets and some Ducks also are easier to capture in flight but note than certain duck species really pick up speed very soon after take-off.  That initial take-off moment in itself is also a nice one to try and capture, watching their body language can help you spot and time the moment to perfection.  If there is a pair of birds or a small flock, then you can usually assume that when the first one leaves, the partner or rest of the flock will follow suit, making it easy to capture the launch and take-off moment by aiming at the remaining ones.  Gulls and some Kingfishers usually allow for some hovering moments which make them an easier quarry.
The incoming and landing moments are also quite easy to capture.  Try and pick up the bird in the viewfinder whilst it is still at a distance.  This will allow the auto focus of the camera to pick up and track the bird easier, and you can follow it through the viewfinder.  Take shots as it approaches, following its flight path, and remember that they usually slow down when landing, applying air brakes (with their wings) to slow down and land on a perch or skiing onto a water surface; slow down your panning or tracking speed accordingly.

An approaching bird head-on or three-quarter angle will require a faster shutter speed to keep it sharp in the frame than a parallel side-on panning shot.  When going for a parallel panning shot you can set a slower shutter speed, keeping the body and head/bill of the bird sharp, whilst getting some attractive motion blur in the wings and background.  Unfortunately, this is very dependent on conditions at the time, and there is no rule to apply.  Experiment each time, learning the limitations of your equipment and your own capabilities.  Remember which settings worked and which did not under specific conditions.

Fast-flying Yellow-billed Duck at slower shutter speed. Canon EOS 1D MkIV, Sigma EX 120-300 f2.8 OS, 600mm, 1/640, f5.6, ISO 1000

Some birds, like swallows, hunting at a dam or pan will frequently return to the same perch which makes it easier to wait for them and then timing the release of the shutter to coincide with their arrival, making for some nice active moments.
The very fast and irregular flight patterns of Swifts, Swallows, Martins and some of the smaller birds like Weavers and Sparrows make them the most difficult ones to capture. Sometimes when they are flying into the wind they will go slower and when starting a turn will be basically in a slow glide-around, then picking up speed very quickly.  The moment just before that slow turn is where you’ll get the most luck. Luck plays a role, as do higher end equipment and your own level of proficiency.  To quote the world class golfer Gary Player “The more I practise, the luckier I get”.  Makes the perfect statement to consistently capture very nice birds in flight images.  Keep on practising, eventually you’ll be rewarded with a luck shot.

You can also think a little out of the box and instead of capturing fine detail and moments, go for a surreal effect, making colour play a role in your image, typically what you’ll get from sunrise or sunsets.
To summarise – learn your equipment’s capabilities and shortcomings and how to use it all to our advantage.  Study the behavioural characteristics of your subject and how to best use it to your advantage.  Then take all those advantages with a good dose of luck and apply it out in the field.  You may just surprise yourself.  I do so with myself on a regular basis.
Text and photos by Sigma Ambassador, Simon Du Plessis, Actionimage